On the use of Multiple Working Points in Multi hannel ALOHA with Deadlines

This paper addresses the problem of maximizing the apa ity of multi hannel Slotted ALOHA networks subje t to a deadline and a permissible probability of ex eeding it. A previous paper proposed to transmit a non-de reasing number of opies of a message in su essive rounds until su ess or deadline. This yielded a low probability of failure due to the large maximum number of opies per message, with only minimal \pollution" due to the small mean number of opies. In this paper, we examine another way of implementing variable resour e expenditure in di erent rounds: the hannels are partitioned into groups, one for ea h round (until the deadline), and the hannels used by later rounds are operated with lower o ered loads. These Multiple Working Point (MWP) poli ies are shown to attain a lower apa ity than the optimal Multi opy (MC) s heme. Combining the two to form an MC-MWP s heme slightly improves apa ity over MC-SWP. The SCMWP approa h an be more attra tive when using a single transmitter per station be ause, unlike MC, transmission time is not prolonged. Therefore, as the trend from high orbit satellites to networks with lower propagation delays ontinues, Multiple Working Point poli ies should be ome of more interest.